Focusing device



A. F. JOBKE.

FOCUSING DEVICE.

APPLICATION FILED AUG-11,1920.

Patented Dec. 6, 1921.

INVENTOR:

UNITED STATES AUGUST F. JOBKE, OF PITTSBURGH, PENNSYLVANIA.

FOCUSING- DEVICE.

Specification of Letters Patent.-

Patented Dec. 6, 1921.

Application filed August 11, 1920. Serial No. 402,862.

To all whom it may concern:

Be it known that I, AUGUST F. Joann, a citizen of the United States,reslding at Pittsburgh, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Focusing Device, of whichthe following is a specification.

My invention relates to a focus ng device, the object of which is toautomatically keep a photographic lens, a plane surface corresponding toan object to be pro ected and a plane surface corresponding toa screenor projecting surface in such positions relative to one another, thatthe image produced through the lens is sharp at any ratio ofmagnification as well as reduction,

Another object of this invention, 1s to make it adjustable to such anextent as to render it applicable not only to the use of a single lensof a certain focal length, but to the focal length of any other lenschosen, thus giving it a usefulness highly desirable in all kinds ofreproduction, and facilitating its manufacture.

Being based on a simple geometric configuration, this invention permitsan exact adjustment of its several elements, and

therefore the most accurate results can be obtained through itsapplication.

I attain these objects by applying a mechanism, the principal part ofwhich is a right angle lever, or for certain purposes an equivalent ofthe same, and I use the angular position of the right angle leverrelative to the optical axis of the combination to establish bothconjugate focal distances.

The nature of my invention will be more fully disclosed and madeunderstood in the following description, where reference is had to thedrawing in which:

Figure 1 showsin a diagrammatic manner the different parts whichconstitute a projection-arrangement with the focusing device and thearrangement to change it for different focal lengths.

Fig. 2 shows a section through an adjustable connecting link.

Owing to the varied uses this invention may be put to in connection withlenses, I deem it reasonable to describe it only with reference to theelements, which are necessary for projection, not referring to any formof camera or projection-machine. As such, 0 in Fig. 1 denotes an objectto be projected, L a lens used for producing an image thereof, and S aprojection screen or sensitive surface to receive the projected image.

A right angle lever ACB, having its fulcrum adapted to slide also on aline parallel to the optical axis in the plane referred to. Connectlnglinks AS and B0 respectively, the length of which is equal to the focallength of the lens, connect the object O and screen S to the slidingbearings on the lever arms.

Any angular change of the right angle lever relative to the o thepositions of O and S in such a manner that their distances from the lensare conjugate focal distances representing a distinct ratio ofprojection, which is magnification, 1f SL is the major conjugate focaldistance and reduction in the opposite case. When ACE is an equilateraltriangle, then AL -LB: the focal length of the lens and S and O arelocated twofocal. lengths from L; this condition corresponds toprojection or reproduction in the same size.

Geometrically the action of the lever is readily understood, if weconsider the rectangular triangle ACB, in which AB is the hypotenuse.and the middle proportionate between the two sections of'the hypotenuse,AL and LB. In other words, the two sections are reciprocals of eachother relative to the focal length and are termed the extra-focaldistances. Since the dimension of the major conjugate focuszf (n+1) andthe minor conjugate focus =f(% 1 where f the focal length of the lensand nzthe factor of magnification or its reciprocal for reduction, wecan readily see that the first members in both brackets are determinedby the position of the right angle lever, while the second members areprovided by the connecting links SA and B0.

While these connecting links may be connected with one arm each of thelever, which would place the fulcrum C in a plane through the opticalcenter of the lens normal to its axis, they may be replaced by links,the sum or difference of which is equal to two focal lengths, or by onelink of the same total dimension, either at A or B.

If the arms of the right angle lever are of equal length, sufficientlylong to provide for CL is then normal to the same.

ptical axis will change the major conjugate focal length on either sideof the lens at a maximum ratio of projection, the combination is adaptedto en large or reduce at this ratio, 2'. a, for a facto of n thetotalrange is 12?.

In many cases, particularly for commercial purposes, Where onlyenlargement or reduction is intended, the lever can be modified so thatthe lever arm, adjusting the minor conjugate focus, is provided tobe ofshorter length, since it has to move the object within the distance ofone focal length. With a reproduction of full size, its dimension fromthe fulcrum C to the center of the sliding hearing (A or) B is equal to1.414 focal len ths of a lens of longest focus.

iscussing now the adjustability of the focusing device to therequirements of lenses of different focal lengths, reference may be hadto Fig. 1, where C, may be the location of the fulcrum of the levercorresponding to a focal length f, of a lens at L. For the same ratio ofreduction we have a triangle A,C,B,, which is similar to ABC. A and Bare the new locations of the sliding bearings. The ratio of A L and LBremains therefore the same, but the planes S and 0 require relocation toobtain the lengths f, for the connecting links 5 A and B 0 Obviously thefulcrum C will have to be varied along the normal CL when a connectinglink :f is provided at each arm of the lever, to keep the conjugatefocal len hs in the same proportions, as Fig. 1 emonstrates. The anglebetween CL and AB varies between 90 and 45 for a cor responding decreasefrom a focal length of the connecting link on the same side. An angle of45 will then correspond to the length of the coordinate link being equalto zero, while. the opposite link will be equal to two focal lengths.

The links SA and B0 may be adjusted simultaneously with the location ofthe fulcrum C. As an example of the means applicable a screw Z is shown,which may be turned by means of the knurled head Y, and by means of anut moves the pivot C up or down as required. A miter-gear set Gtransmits the movement of the screw to the shaft X which must be longenough to reach into sleeves U which are parts of the links SA and B0.In keying the shaft X and the sleeves loosely, angular movement betweenthem is prevented and only axial sliding made possible.

External thread on the sleeves U and in ternal thread on the secondmembers V of the connecting links of the same pitch as that of the screwZ places the planes S and O in the right focal planes relative to thefulcrum C. It has to be kept in mind, that,

if Z and B0 have right hand thread, the

thread on'SA. must be left hand. Fig. 2 shows a section through aconnecting link.

The extrafocal distances and conjugate focal lengths are shown asmultiples of the respective focal lengths for the convenience ofinspection, assuming the connecting links are equal to one focal length.

Havin thus described my invention, what I c aim and desire to secure byLetters Patent is 1. In a focusing device a lens and a right anglelever, having its fulcrum at the right angle, stationary relative to thelens in the direction of its axis, variable relative to and located froma plane through the optical axis at.a distance of the focal length, thearms of the lever at the intersection with the said plane on a parallelto the optical axis cutting at extra-focal distances for the focallength from the intersection of a normal from the fulcrum to the saidparallel.

2. In a focusing device a lens and a right angle lever having itsfulcrum at the right angle, stationary relative to the lens in thedirection of its axis, variable relative to and located from a planethrough the optical axis at a focal length, and a pivoted hearing oneach arm of the lever adapted to slide on the arm and on a parallel tothe optical axis in the said plane.

3. In a focusing device for an optical combination, consisting of anobject, a lens and a plane representing a projecting surface, a rightangle lever, having its fulcrum at the right angle, stationary relativeto the lens in the direction of its axis, variable relative to andlocated from a plane through the optical axis at a focal length, apivoted sliding bearing on each arm of the lever, adapted to slide on aparallel to the optical axis in the said plane, and means adapted toconnect the object and projecting surface with the sliding bearings, sothat the distance between them is equal to the two conjugate focallengths.

4. In a focusing device for an optical combination, consisting of anobject, a lens and a plane representing a projecting surface, a rightangle lever, having its fulcrum at the right angle, stationary relativeto a lens in the direction of its axis, variable relative to and locatedfrom a plane through the optical axis at a focal length, a pivotedsliding bearing on each arm of the lever, adapted to slide on a parallelto the optical axis in the said plane, means adapted to connect theobject and projecting surface with the sliding bearings, and means tovary the position of the fulcrum relative to the said plane through theoptical axis.

5. Ina focusing device for an optical combination, consisting of anobject, a lens and a plane representing. a projecting surface, a rightangle lever having its fulcrum at the 1,see,a47

right angle a pivoted sliding bearing on each arm of the lever, adaptedto slide on a parallel to the optical axis, means to vary the position,of the fulcrum, including a nut supporting the latter and a screw alonga.

line in a plane through the optical center of the lens at an angle tothe optical axis, and means, including adjustable connecting links,adapted to connect the object and projecting surface with the slidingbearings, their length being equal to two focal lengths.

6. In a focusing device for an optical combination, consisting of anobject, a lens and a plane representinga pro ecting surface, a rightangle lever, having its fulcrum at the right angle, a pivoted slidingbearing-on each arm of the lever, adapted to slide on a parallel to theoptical axis, means to vary the position of the fulcrum, including a nutsupporting the latter and a screw, adaptec to be guided on a line normalto the optical axis, and means, includin adjustable con necting links ofone i length each, to connect the object and projecting surface to thesliding bearings to establish conjugate focal lengths between theobject, the lens and the projecting surface.

In testimony whereof I aflix my signature.

AUGUST F. JOBKE,

